Global warming is thought to be at least partly caused by emissions of waste industrial gases like carbon dioxide, produced by burning fossil fuels like coal, oil and natural gas.
These emissions trap solar radiation and produce a greenhouse effect.
Methane and nitrous oxide emissions from agriculture (ruminants and manure) make up 8% of greenhouse gases.
Controls on sulfur dioxide emissions reduce a balancing cooling effect.
Global warming already causes more frequent El Nino appearances, receding shorelines, longer warm seasons, and a slower earth spin.
It affects habitats and threatens marine life.
If emissions are not reduced, average surface temperature will rise 2-6 degrees over the next century, bringing widespread climatic, ecological and economic dislocation.
Floods and droughts will increase in frequency and intensity.
Melting polar ice will cause rising sea levels and coastal flooding.
Malaria will increase.
Rates of habitat loss and species extinction will increase.
Communities will need to adapt to new conditions.
Skeptics argue that human activities have little influence on climate.
Most observed warming is due to natural causes like changes in solar radiation or the circulation of heat-bearing ocean waters.
Measurements taken by satellites have found little temperature rise in the upper atmosphere.
Computer models are unreliable.
Any warming over the next century would be most pronounced in the winter, at night, and in sub-Arctic regions, doing little harm and creating benefits like longer growing seasons and faster plant growth.
Industry argues that reducing the use of fossil fuels would cause economic harm to consumers.
